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Wed, 17 Dec 2025 11:23:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id MoFiO86SQmmQXAAAD6G6ig (envelope-from ); Wed, 17 Dec 2025 11:23:58 +0000 Message-ID: <1c94600d-47eb-40b6-8c7e-fb2cc39e1e4b@suse.cz> Date: Wed, 17 Dec 2025 12:23:58 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: restore 0-handling to zone_set_pageset_high_and_batch Content-Language: en-US From: Vlastimil Babka To: Joshua Hahn , Andrew Morton Cc: Daniel Palmer , Guenter Roeck , Brendan Jackman , Johannes Weiner , Michal Hocko , Suren Baghdasaryan , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox References: <20251217060505.681923-1-joshua.hahnjy@gmail.com> <1cf7675a-2de3-425f-9938-af97f7c6436d@suse.cz> Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <1cf7675a-2de3-425f-9938-af97f7c6436d@suse.cz> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 03B7C40002 X-Stat-Signature: fmmo7b1s8zifquzogmg6mrwb5rnkysfk X-Rspam-User: X-HE-Tag: 1765970641-546163 X-HE-Meta: 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 awBow1g/ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/17/25 12:12, Vlastimil Babka wrote: > On 12/17/25 07:05, Joshua Hahn wrote: >> Commit 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") >> moved the error handling (0-handling) of zone_batchsize from its >> callers to inside the function. However, the commit left out the error >> handling for the NOMMU case, leading to deadlocks on NOMMU systems. >> >> Since in the NOMMU case the reported-to-user batchsize should still be 0, > > Should it? The value is effectively set to 1 despite what zone_batchsize() > returns, because of that adjustment this patch reinstates. Also does anyone > care, really? > >> we would only like the error handling to exist in the callsites that >> set the internal value for the zone (i.e. zone_set_pageset_high_and_batch). >> >> Restore max(1, zone_batchsize(zone)) to the callsite to prevent errors >> on NOMMU systems. > > I would rather make zone_batchsize() for !CONFIG_MMU return 1 instead of 0. Ah looks like you considered it too, initially: https://lore.kernel.org/all/20251211225947.822866-1-joshua.hahnjy@gmail.com/ It makes more sense to me than doing effectively two fixups in the MMU case. >> Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") >> Reported-by: Daniel Palmer >> Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@mail.gmail.com/ >> Reported-by: Guenter Roeck >> Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@roeck-us.net/ >> Signed-off-by: Joshua Hahn >> --- >> mm/page_alloc.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 822e05f1a964..10c1297fd3ea 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -6045,7 +6045,7 @@ static void zone_set_pageset_high_and_batch(struct zone *zone, int cpu_online) >> { >> int new_high_min, new_high_max, new_batch; >> >> - new_batch = zone_batchsize(zone); >> + new_batch = max(1, zone_batchsize(zone)); >> if (percpu_pagelist_high_fraction) { >> new_high_min = zone_highsize(zone, new_batch, cpu_online, >> percpu_pagelist_high_fraction); >> >> base-commit: 40fbbd64bba6c6e7a72885d2f59b6a3be9991eeb >